m4 m4 WHAT IS A TOKAMAK? Graphic: EUROfusion, Reinald Fenke, CC BY 4.0, www.euro-fusion.org

m4 EXPLANATION Tokamak is a Russian acronym meaning donut-shaped vessel surrounded with magnets. The tokamak is the most advanced device towards the production of electricity from fusion energy. It consists of Tokamak itself Heating systems Measurement systems

BASICS OF A TOKAMAK m4 It consists of Metallic vessel to contain the plasma Magnetic field coils to guide the plasma particles generate a current in the plasma shape the plasma Coils Vessel Magnetic field line Plasma Graphic: EUROfusion, Reinald Fenke, CC BY 4.0, www.euro-fusion.org

TOKAMAKS IN FIGURES m4 Size: Radius 0.5 – 6 m Volume 0.01 – 100 m3 Magnetic field 1 – 8 T ~100 thousand times the earth magnetic field Plasma current 0.1 – 8 MA ~100 thousand times the current in a domestic plug Plasma shape – shape of cross section Plasma Elongation Plasma Triangularity Changing the plasma shape changes the plasma properties especially the confinement JET TCV ITER Low Elongation High Elongation Strong negative Triangularity Zero Triangularity Strong positive Triangularity Graphic: Max Planck institute for Plasmaphysics, Reinald Fenke, www.ipp.mpg.de

MAGNETIC CONFINEMENT m4 The combination of the magnetic fields naturally forms a cage-like structure, consisting of a series of nested rings. Since particles of the plasma follow the magnetic field lines, they remain confined in the vicinity of the surface of a ring. Coils Vessel Magnetic field line Plasma Graphic: EUROfusion, Reinald Fenke, CC BY 4.0, www.euro-fusion.org

PLASMA HEATING SYSTEMS Wave heating Injection of high frequency waves (like in a microwave oven but 100-10’000 times more power) Wave – plasma resonance Energy transferred to plasma PLASMA HEATING SYSTEMS Ohmic heating Produced by the plasma current Neutral beam injection Injection of fast particles Collisions with plasma particles Energy transferred to plasma Graphic: EUROfusion, Reinald Fenke, CC BY 4.0, www.euro-fusion.org

PLASMA DIAGNOSTICS MEASUREMENT SYSTEMS m4 It is not possible to insert a thermometer into the plasma … then all systems must be based on natural emission of the plasma (light, particles) interaction with laser light (or particle beams) to measure the plasma density plasma temperature plasma emission … Image: EUROfusion, CC BY 4.0, www.euro-fusion.org

m4 PLASMA DIAGNOSTICS Now: several systems to diagnose the plasma, for scientific exploitation Later: fewer systems in a commercial reactor, for control only 30 Image: EUROfusion, CC BY 4.0, www.euro-fusion.org

Half-silvered mirror or Beam splitter PLASMA DENSITY Interferometry One laser beam Split into two beams – One through the plasma – One outside the tokamak Recombine the beams Interferometry fringes When the plasma density increases, it delays the beam crossing the plasma and then induces interferences when it is recombined with the other beam. Counting the interferences gives the plasma density. Detector Plasma In phase + = Out of phase + = Laser Half-silvered mirror or Beam splitter Image: Swiss Plasma Centre, EUROfusion

m4 THOMSON SCATTERING Laser light is scattered by the electrons in the plasma. Due to Doppler effect, the frequency of the scattered light is shifted. Collected light shows a continuous spectrum around the laser frequency. The width of the spectrum increases with electron temperature. Image: EUROfusion, CC BY 4.0, www.euro-fusion.org